Manipulation of printing blankets

ABSTRACT

A container for a printing blanket comprises a cassette of dimensions sufficient at least to contain a printing blanket in wound form. The cassette comprising a casing of generally cylindrical shape having a longitudinal opening for sheet-form egression of a printing blanket from within the cassette. In one preferred embodiment, the cassette has a pressure slide attached to or integral therewith adjacent to the longitudinal opening, for pressing a printing blanket on a press cylinder when the blanket is fed onto the cylinder. The cassette is employed in the manipulation of large adhesive-backed printing blankets for web-feed offset printing presses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to manipulation of printing blankets.

2. Discussion of Prior Art

A common means for securing an offset printing blanket onto a presscylinder employs a tensioning ‘lock-up’ device located within thecylinder body. Employment of such a device usually necessitates a gap inthe usable printing area of the cylinder and furthermore tends topromote undesirable vibration during operation of the printing press,especially at high-speed printing.

It has been proposed to avoid vibration by providing a ‘seamless’ orendless blanket on the printing press cylinder. Typically such blanketsare supplied on a metal sleeve to be fitted on the cylinder. Althoughsuch blankets may be feasible for newly manufactured presses whereinmeans for ease of removal of the cylinder or sleeve may be incorporatedin the design of the press, they are not a practicable option for themajority of existing presses. Moreover, a disadvantage of such blanketsis the high cost of producing individual blanketed sleeves or cylindersin comparison with the cost of producing a sheet-form (open-ended)blanket for application to replace a worn or damaged similar blanket onan existing cylinder in the press.

In some relatively small offset printing presses (such as those used forprinting stationery and business forms), in which the printing cylindertypically has a circumference of the order of 30 cm, a negligible gap inthe usable printing area is achieved by securing a sheet-form printingblanket on the cylinder by means of an adhesive which typically is inthe form of an adhesive coating on the back of the blanket sheet and maybe protected by a releasable cover sheet until the blanket is applied tothe cylinder.

Although adhesive-backed printing blankets are used for small presses,generally they have not been used for large web-feed printing pressesowing to problems in handling and mounting large sheets ofadhesive-backed blanket. Problems include manual handling difficultiesand safety risk to persons manipulating a bulky adhesive-backed blanket,the risk of contamination of the adhesive backing during manipulation,and the need for the initial positioning of the blanket on the cylinderto be accurate since the capability for position-adjustment afterinitial application usually is extremely limited or non-existent withoutdetriment to the blanket or the adhesive bond.

In large high-speed printing presses, such as those used in thenewspaper and magazine printing industry, typically the printing blanketrequires to be replaced owing to wear at frequent intervals, forinstance every one to three months. Speed of application of areplacement blanket onto the cylinder is especially important in thenewspaper and magazine printing industry where a long down-time of aprinting press could be highly detrimental to meeting distributiondeadlines.

SUMMARY OF THE INVENTION

An object of the present invention is the provision of means tofacilitate manipulation of large adhesive-backed printing blankets toenable their commercial application to large printing press cylinders.

A further object of the invention is the provision of means for enablinga printing blanket, especially an adhesive-backed printing blanket, tobe applied to a press cylinder accurately with increased speed.

A further object of the invention is the provision of means for enablingadhesive-backed blankets to be stored, transported, handled and appliedeasily, accurately and quickly, with minimal risk of contamination ofthe adhesive, damage to the blanket and trapping of air between theblanket and the cylinder.

The invention is beneficial for blankets of all sizes, with or withoutan adhesive backing. However, the benefits are especially advantageousin respect of large adhesive-backed printing blankets for web-feedoffset printing presses.

According to one aspect of the present invention there is providedmanipulation means for a printing blanket, comprising a cassette ofdimensions sufficient at least to contain a printing blanket in woundform, said cassette comprising a casing of generally cylindrical shapehaving a longitudinal opening for sheet-form egression of a printingblanket from within the cassette.

According to another aspect of the invention there is provided a methodof mounting a printing blanket on a printing press cylinder, whichcomprises feeding the blanket onto the cylinder from a cassettedescribed in the immediately preceding paragraph.

The cassette casing may have a substantially continuous cylindrical wall(apart from the opening for egression of the blanket), or it may have adiscontinuous cylindrical shape, for instance a frame structure.

The cassette may be open or closed at one or both of the casing cylinderends. At least one of the ends may be closed by a cap which is removablefor insertion of a blanket into the cassette.

The blanket suitably is in roll-wound form inside the cassette.Preferably the outer, leading, end of the contained blanket ispositioned adjacent to the longitudinal opening which suitably is anelongate gap or slot in the casing wall.

If desired, the cassette may include a spindle, which may or may not berotatable, about which the blanket is wound. The longitudinal centralaxes of the cassette casing and spindle may be coincident or parallel.For instance, the spindle axis may be off-set away from the casing axisalong a plane passing through the position at which the blanket beginsto diverge from the blanket roll when the blanket is fed through thelongitudinal opening.

Preferably the cassette casing should have sufficient rigidity to retainits shape during handling, feeding and loading of the blanket. Suitablematerials include plastics and metals.

The cassette may be reusable or disposable.

For feeding a blanket from the cassette onto a press cylinder, thecassette should be mounted in a set relationship to the press cylinder.For instance, location means may comprise an axial spigot extending fromeach end of the cassette for location in a hole, slot or cup on thepress structure, if desired in conjunction with detent means to preventthe spigots from becoming dislodged accidentally.

Suitably the cassette is mounted such that its longitudinal axis isparallel to that of the press cylinder onto which the blanket is to befed.

The blanket may be fed from the cassette onto the press cylinder simplyby pulling the leading end of the blanket through the longitudinalopening of the cassette, positioning the leading end of the blanketsecurely on the surface of the cylinder, and rotating the cylinder topull the rest of the blanket from the cassette onto the cylindersurface.

The cassetted blanket may be of a length to fit the cylinder exactly orit may be longer than the circumference of the cylinder and then trimmedto the correct length, e g by cutting or stamping on the cylinder.Alternatively the cassette may contain two or more blanket pieces forapplication to the cylinder as one piece after another in line or as onepiece on top of another.

When the blanket has an adhesive-coating protected by a releasablesheet, the protective sheet suitably is removed from the blanketcontinuously as the blanket is fed from the cassette. This may be donemanually or by a separator blade and the released sheet may be collectedin a bin or by winding on a roller.

Preferably the blanket is pressed onto the cylinder during itsapplication in order to ensure good bonding contact and to preventtrapping of air between the blanket and the cylinder.

If desired, the blanket may be pressed onto the cylinder manually, suchas by moving a roller under pressure over the blanket on the cylindercontinuously from the line of initial contact.

However, a preferred pressure means comprises a dedicated pressureroller or a pressure slide (skid), mounted with its longitudinal axisparallel to those of the cassette and cylinder and at a set distancefrom the cylinder surface at or immediately after the line of initialcontact of the blanket with the cylinder. The maximum distance of thepressure roller or slide surface from the cylinder surface should not begreater than the thickness of the blanket being applied and may beadjustably set to apply a predetermined pressure on the blanket.

The pressure slide may have a curved surface, at least at its edgeportion proximate to the casing opening, to facilitate smooth sliding ofthe blanket over the slide surface. The pressure slide may be attachedto the press structure or, preferably, may be attached to, or beintegral with, the cassette casing.

The pressure means may be mounted to be guided towards and away from thecylinder as required.

If desired, the leading end portion of the blanket may be located on thepressure means, such as by use of a relatively weak adhesive (e g doublesided adhesive tape), prior to mounting the pressure means at itspressure distance from the cylinder. The pressure means is then moved toits pressure distance with the leading end portion of the blanketbetween the pressure means and the cylinder. Such a procedure may beuseful for reducing the risk of operator contact with the adhesivebacking on the blanket since the protective sheet may be released fromthe leading end portion of the blanket more easily while the end portionis supported on the pressure means. The weak adhesive employed to locatethe blanket end portion on the pressure means should be capable ofreleasing the blanket from the pressure means when the cylinder issubsequently rotated during feeding of the blanket onto the cylinder.

After application of the blanket onto the cylinder, usually the cassetteand, if employed, the pressure means are moved away from the cylinderand may be removed altogether from the press frame.

The present invention is suitable for employment in conjunction with theinvention described in our co-pending patent application filed on Dec.29, 1997 entitled ‘Printing Press Cylinders’ U.S. Ser. No. 08/952,065.When used in conjunction with the invention described in said co-pendingpatent application, the leading edge of the blanket may be located alongthe nearer edge of the slit in the cylinder surface or overlapping theslit and then trimmed along the slit.

The adhesive employed for attaching a blanket to a press cylinder mustbe stable at the temperatures created during high speed running of theprinting press and should be resistant to solvents employed for cleaningthe blanket.

Preferably the adhesive should be such as to enable removal of a worn ordamaged blanket by peeling off the cylinder with no or minimal adhesiveresidue left on the cylinder surface.

The adhesive layer should be of low thickness and of uniform consistencyin order to avoid conferring even small aberrations on the total blanketthickness.

Accordingly, a contact adhesive usually is employed and typically suchadhesives have a high initial bond strength which resists adjustment ofthe position of the blanket after contact with the cylinder. However,other types of adhesive, for instance a settable adhesive (e g heat- orradiation-settable) or a reaction adhesive (e g comprising apressure-rupturable microencapsulated reactant), may be employedprovided that they satisfy the requirements for a printing operation.

The adhesive typically is employed as a pre-coating on the cylinder-side(back) of the blanket and is protected by a releasable sheet of flexiblematerial such as paper or plastics film until immediately prior toapplication of the blanket to the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated, by way of example only, in theaccompanying drawings, FIGS. 1 and 2.

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS

FIG. 1 shows a cassette 1 in accordance with the invention, comprising acylindrical casing 2 having a longitudinal opening 3 and (optionally) aspindle 4. The cassette is shown in mounted relationship with a printingpress cylinder 5 and a pressure roller 6. An adhesive-backed printingblanket 7 with a releasable protective cover sheet 8 on the adhesivebacking is in wound-roll form inside the cassette. The leading endportion 9 of the blanket 7 is shown as having been fed Out of thecassette through the opening 3, around the pressure roller 6 and ontothe cylinder 5. The protective cover sheet 8 is released from theblanket continuously as the blanket emerges from the cassette, and thepressure roller promotes firm even adhesion of the blanket to the presscylinder surface as the cylinder is rotated about its central axis.

FIG. 2 shows an alternative embodiment of the invention, in which likenumerals denote features similar to those of FIG. 1, except that insteadof the pressure roller 6 of FIG. 1 there is a pressure slide 10 which isintegral with the cassette casing 2.

What is claimed is:
 1. A cassette for housing and applying an adhesivelybacked printing blanket to a printing press cylinder to which saidblanket is to be adhesively bonded, said cassette comprising: a cassettecasing having internal dimensions sufficient at least to contain saidadhesively backed printing blanket in wound form, said cassette casinghaving a generally cylindrical shape; said casing having a longitudinalopening for sheet form egression of said printing blanket from withinthe cassette for application to said printing press cylinder.